What is knowledge but memory -- with maybe some organization of the facts thrown in? And of what use is any knowledge if we can't grasp the meaning of things, the nature of the actual world we're living in? What if, in our acquisitive search for more and more knowledge, we miss the point of living altogether?

This very beautiful novel is about Sherlock Holmes -- or, more accurately, about the human being who lives behind the public mask of Holmes as that mask begins to crumble. Watson is long dead, and the aged Holmes has retired to the country, where he pursues an obsessive interest in raising bees. He tells himself it's because of the health benefits of royal jelly, but he also derives a strange comfort from the communal lives of the bees themselves. They live an existence of predictable, perfect order -- in contrast to human beings, who strive so mightily to imbue their activities on this earth with meaning even as order lies quite beyond their grasp.

Holmes, at 93, concentrates first on himself, conscious of a capricious memory and a body that is failing. He relies on two canes for walking. He tries to keep up with his paperwork, which never seems to come under control. He is deluged by requests, most of them venal, vapid or stupid, and he consigns them to the fire in his study. But some are more disturbing: Since he is Sherlock Holmes, surely he can explain why such-and-such an awful thing has happened? Of course, he can't, and these queries end up in the fire, too.

A very few of these letters show fine intelligence, though, and a strong wish to communicate about subjects that interest the retired detective. A Mr. Umezaki of Kobe, Japan, has written of the healthful, life-prolonging properties of the prickly ash, which grows in his neighborhood, and the novel begins as Holmes returns from visiting his correspondent. His journey has included a trip to Hiroshima. (The ancient Holmes has lived to see 1947, just two years after the calamity of the bomb.) He's home now, in his country house; his only company is his widowed housekeeper, Mrs. Munro, and her 14-year-old son, Roger, who has come to share his passion for beekeeping.

"A Slight Trick of the Mind" unfolds in three parts, two from the past, one from the increasingly dreamlike present. Holmes has been compelled to write one more story of his early days (though he laments Watson's absence as a scribe). The great detective recalls a seemingly trivial case involving a Mrs. Keller, a young wife who has miscarried two children and been consumed by melancholy. She has been lately comforted by the music of the "armonica," an instrument played by the twirling of glasses and thought by some to carry an occult power. No crime is involved -- just a mystery, supposedly soon solved.

In the shimmering present, Holmes wanders in his apiary with young Roger, sharing companionable silences. Roger sneaks into Holmes's study when he is away; more remarkably, Holmes visits the boy's room when he's away. A gradual, yearning fondness -- though always proper and full of seemly reticence -- springs up between them.

And Holmes recalls his recent sojourn to Japan. Umezaki, it turns out, hadn't been all that interested in the beneficial attributes of prickly ash. A homosexual living with both his partner and mother, he believed that Holmes could solve the mystery of his missing father. In successive, brooding scenes, the mystery is posed and again -- perhaps -- solved.

These three different-aged men -- the ancient Holmes, the middle-aged Umezaki, the adolescent Roger -- inhabit worlds that shut women out. "Since you went," Mrs. Munro says peevishly to Holmes of her son, "he's cared more for them bees than his own mother." Women in this story have nothing to live for without their men. But men may pay a terrible price for their self-sufficiency. They may make "observations on a vast number of things," but in doing so, not see the forest for the trees. They may cut themselves off from life's only real meanings, from intimacy and love.

This is a lovely, tenderhearted book, full of reserve, good manners, elegance of feeling. It's what a novel should be. You don't read it to be "improved" but for the plain joy of seeing what the language can do in the hands of an affectionate, very accomplished writer.